Congratulations on your 25th! My wife and I just celebrated our 40th last year and a cruise is an awesome way to celebrate!!
Alaska is amazing and no matter what you decide to do, I know you'll love it.
My best advice is to definitely look at booking independent excursions and not booking through the cruise line - they charge more, are very regimented, and always very crowded. Whereas often with an independent, you may be the only one on the excursion, will usually pay less, and they are almost always very flexible so you have more fun.